It's a V8 with a single large pipe in the center section of the car that divorces into two 3.5" pipes in front of the rear axle and has two MagnaFlow "straight thru" mufflers at about the rear axle, one on each side. Downstream of the rear axle, there's two divorced 3.5" pipes that both go to the same side into a cavity next to the bumper. I need to make a muffler for that non-standard weird space under the trunk right next to the driver side bumper. Would need to flow well but suppress some noise, at least under 2500 rpm.

It's an updated version of this exhaust below (going from 3.0" to 3.5" pipes and a single oval center section not visible in the photo). The last section needs a muffler next to the battery box. In terms of flow, it needs to flow about 1000hp worth of exhaust with minimal back pressure, so I'm thinking dual 3.5" inlet and single 5.0" outlet sort of deal, or something with 2x3.5 and/or 1x5.0". Any ideas how to make the quietest possible muffler there? Weight is pretty much irrelevant but can't be restrictive or hang too low.

P1000505.JPG

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[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

I would build a anti-reversion termimation style box. Size and stiffness of material makes a difference. Bigger may be better in this case. I would bring lead pipe in about 3" past case edge. I would make a long taper to the exit. I would measure db of sound the way the system is now at specific rpms. 3db reduction in sound represents one half the sound energy. So measuring before and after may be helpful.

Carnut1 wrote:I would build a anti-reversion termimation style box. Size and stiffness of material makes a difference. Bigger may be better in this case. I would bring lead pipe in about 3" past case edge. I would make a long taper to the exit. I would measure db of sound the way the system is now at specific rpms. 3db reduction in sound represents one half the sound energy. So measuring before and after may be helpful.

I agree on measurements to verify after the fact whether its doing anything. If I have the measurements for the current system, though, is there something in those measurements that I could reasonably take into account in designing the muffler?

D.V. artwork but you can get the idea of what I am saying. Top left corner of picture. Terminator box can be rectangular on the outside and tapered on the inside. I have no scientific proof this will reduce sound pressure level that you want. I built one for a Mercury tracer 1.6l I found myself owning in the 90's. The engine had a stock cam, but ported head, ported intake and exhaust manifolds, ported throttle body and custom mass air box and air plumbing. Even though it had a stock cam the engine liked the anti-reversion muffler and had no downsides. A far cry from 1000hp! Thanks, Charlie

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With a 1000hp I understand the op's problem. Hell the old work truck can turn on car alarms from 20' away and it has ganged hooker aero chambers down to a single 3" outlet. (Not nearly the power either) Muffling a 1000hp and not losing a good amount of that power is a challenge. That is why I figured the termination box would be a 3db help. Thanks, Charlie

Your limiting factor will of course be space available beneath your car and factors affecting routing of your exhaust system. I have built several pulse wave termination systems based upon David Vizard's recommendations in his writings. You may be able to achieve all or at least most of the recommended volume and favourable results if you design and execute your exhaust system with David's design parameters in mind.

Fortunately, we were building a system for a full sized pickup and had more room to work with and were dealing with less power (around 480 HP at the flywheel), but it was a learning process, nonetheless.

Some things we learned and ran up against......

* Allow end of collectors to extend 2" to 3" into termination chambers. Same for exit pipe at opposite end.

* Ideally, you want each termination chamber to have volume equal to twice the displacement discharged into it. More doesn't hurt and even if you cannot get more than 75%, its worth the effort.

* Muffler(s) should be located downstream of chambers (can be directly behind chambers or anywhere between ends of chambers and ends of exhaust system.

* Chambers can have round, oval, square or rectangular cross section. And a square cross section of same size as a round cross section will obviously have greater interiour volume for same length. However...... In actual practice, we found straight sided (square or rectangular) chambers of same wall thickness are more likely to flex, work harden and be affected by metal fatigue over time than round or oval cross sections.

* The first chambers we made were from 0.060" thick sheetmetal and of square cross section. Drone inside cab at highway speeds would drive you bonkers on long (over 30 minute) trips. And although seams were welded properly, we found linear defects (cracks) beginning to form near center sections after only a few week's use.

* Next 'fix' we tried involved constructing same size and shape chambers from .090" thick sheetmetal and adding strengthening gussets inside every 9". We also bent metal so that seams overlapped metal it would be welded to by 1/4" and the only butt welds were to the end caps, which we made of thicker (0.120") metal. These chambers were very heavy and we had to double up on hangers to support them, but seemed to stop much of the flexing and we saw no cracks develop in welds nor in bends. Drone inside cab at highway speeds was slightly less, but was still an issue. Until we built the next chambers from round tubing, we resorted to wrapping the square cross section termination chambers with some sound absorbing heat resistant material my friend had and securing it with metal banding material. There was still some drone, but not as bad.

* 3rd set of chambers we built from round tubing and made them longer to get the recommended interiour volume. We had 3-1/2" collectors dumping directly into 5" dia. chambers. Drone was less, but still an issue at highway cruising speeds. No problems with walls of round chambers flexing nor any metal fatigue nor weld cracking. Also much lighter than our heavy wall square chambers had been.

* Final configuration...... We pulled round termination chambers and hand drilled beaucoup 3/16" diameter holes in them (360 degrees on 3/4" spacing to within 1" of each end). This took a while and was no fun at all. When done, we made new end caps (like large flat washers) to accommodate larger outer shell 7" in diameter, slid one over front stub and welded it in place, leaving original cap and the tubing we had drilled in place. Slid outer shell over tubing that we drilled and welded outer shell to front end cap. Then went to a machine shop where they had lots of stainless steel shavings they had saved for us and packed them into the annular space between tubing we drilled and new outer shell using a piece of 3/4" square bar stock a couple of feet longer than our new outer shell. Once we had it packed tight in each, we slid the washer shaped rear end cap piece over stub and welded it in place. The end result was that we made our termination chambers double as straight through steel packs in addition to the DynoMax Super Turbo mufflers we already had just ahead of rear bumper. These DynoMax mufflers were sized for flow and gave us the 2.2 cfm per HP recommended by David Vizard for zero sum loss muffled exhaust system. It was still pretty throaty when you got on it but was quiet enough not to drive you nuts on long trips and not loud enough to draw unwanted attention from police.

* Crossover (balance) pipes connecting left and right bank...... We found no advantage between 'X' type and 'H' type so long as 'H' type was same size as collectors. Crossover pipe can be placed anywhere after primaries enter collectors and it can even be placed between termination chambers if you wish. We placed ours about 6" behind front of termination chambers. Later added a 2nd crossover joining left and right side tailpipes behind chambers in area just before top of bend going over rear axle. Each crossover pipe seemed to help lower noise level a bit and smoothed out exhaust note some, as well.

* One thing we found on chassis dyno regarding full length muffled exhaust was that if your pipe size is sufficient for power generated but you cannot get flow you need through mufflers any other way...... By using tube size increasers/reducers (like a bell reducer), if you install free flowing mufflers having one size larger internal flowpath than pipe system size...... They will flow same as if you ran straights (no mufflers). But they will be louder than mufflers same size as pipe system.

You may also want to look into chambered exhaust tubing and straight through mufflers/resonators with packing. Check out larger size mufflers with packing listed for diesel applications......

Enigma's post was awesome! I believe you will probably have a very hard time stuffing a large enough case in such a small area near the bumper too. At least without pooching the entry angles to get it all stuffed in there anyways. Radii's needed for routing are pretty important too, if you catch my drift.

Personally, I'd try to use more of the available space up in the front section before looking for more sound reduction real estate at the rear. Dead headed J-bends located anywhere mid section can also help tune and refine the sound to be less aggressive to eardrums too.

Just a muffler comment, dual 2.25 Walker Super Turbos were loud and had a horrendous 2000-2500 rpm drone on my turbo Regal. Changed to a dual 2.5 Walker Ultra Flow system and it was quieter everywhere and no drone at all. I've been told the Magnaflows are as good but no personal experience with them. Also I believe multiple small pipes are much quieter than one big pipe. Every dual 2.5 system I've heard on a Regal was way quieter than a single 3 inch system, both with UF mufflers.

I don't see here much about the actual acoustics of muffler design. That is the point, basically getting the generated exhaust waves to get 180Deg out of phase and then canceling, I thought. The issue becomes which frequencies to tune for and cancel, since wideband out of a single muffler per path has many drawbacks. And the issue is as with everything else we toy with, "everything effects everything else", point being I suspect very small changes in any one of thousands of parameters will change ones's outcome, RPM, tube lengths, number of chambers, chamber volumes, exhaust velocity, back pressure, temperature, orientation, material etc, etc. Is a very moving target, I can't see how what works for one set-up can with any certainty work well for another, and only in the best of situations only point in a favorable direction. Best aspect, when we are finsished with our solution, we all suffer from varying degrees of confirmational bias, and go about our merry ways.